DOEACC Online E-Books and Notes

Computer Abbreviations and Names

2008-12-07T12:01:00.000-08:00

Entire area desktop
Below line Task bar
Small Bar Icons
Left down Button Start Button
Right tray on Task Bar System tray
Picture set on desktop Wallpaper
To change date and time double click on time on system tray on desktop. Right click and adjust.
On right click menu shown called pop up menu.
10% of hard disk is used as recycle bin.
Try to save application programs in drive C. my documents comes under this drive. Much memory of this drive can reduce the speed of PC. A desktop item also comes under this drive.
To see windows simultaneously go to task bar and rat clicks and select horizontal or vertically tie.
Serially bar are called as Title Bar, Menu Bar, Standard tool bar, Address toll bar, Task pan (left side of screen).

shortcut for microsoft words

2008-10-24T03:08:00.000-07:00

cntr+A	Select all
cntr+B	bold
c	copy
d	format dialog box
e	center line
f	find
g	go to
h	replace
i	italic
j	justify
k	hyperlink
l	left align
m	new slide
n	open new window
o	open a document
p	printer
q	remove paragraph
r	right align
s	save
t	format and character
u	underline
v	paste
w	close window
x	cut
y	redo
z	undo

MOVING THE TEXT

Steps to move the text (generally the paragraphs),

·    Block the text to be moved.

·    Select Edit -> Cut (or press Ctrl+X).

·    Click in a new place, where the blocked text should appear

·    Select Edit -> Paste (or press Ctrl+V)

COPYING THE TEXT

Steps to copy or duplicate the text,

·    Block the text to be copied.

·    Select Edit -> Copy (or press Ctrl+C).

·    Click in a new place, where the blocked text should be copied.

·    Select Edit -> Paste (or press Ctrl+V).

UNDO, REDO AND REPEAT

To undo the previous work select, Edit -> Undo or press Ctrl+Z.

To redo the previous action, select Edit -> Repeat or press Ctrl + Y.

FUNCTION, ICON AND SHORTCUT KEYS

Function	Icon on Formatting Toolbar	Shortcut keys
Bold facing	Bold icon	Ctrl + B
Italicising	Italic icon	Ctrl + I
Underlining	Underline icon	Ctrl + U
Size	Size box	Ctrl + Shift + P
Text font	Font box	Ctrl +Shift + F

SOME SHORTCUT KEYS FOR FORMATTING

Short cut keys	Action	Example
Ctrl + Shift + A	All caps (All upper case)	ALL CAPS
Ctrl + Shift + K	Small caps	small caps
Ctrl + U	Underline all	Underline all
Ctrl + Shift + D	Double underline	Double underline
Ctrl + Shift + W	Word underline	Word underline
Ctrl + B	Bold	Bold
Ctrl + I	Italic	Italic
Ctrl + Shift + H	Hide
Ctrl + =	Subscript	Subscript
Ctrl + Shift + =	Superscript	SuperSCript
Ctrl + F	Find and Replace
Ctrl + P	Print menu
Ctrl + space bar	Reset character
Ctrl + [	To decrease the character size one point at a time
Ctrl + ]	To increase the character size one point at a time
Ctrl + Shift + <	Reduces the font by point sizes as displayed in the formatting toolbar.
Ctrl + Shift +>	Increases the font size by point sizes as displayed in the formatting toolbar.

Reinstalling System

2008-10-20T02:39:00.001-07:00

Reinstalling System Restore

Click Start, Run and type %Windir%\INF
Locate the SR.INF file. If you have configured Windows Explorer to hide known file extensions, the file may show up as SR. To see the file extensions for all file types, then try this:

On the Tools menu in My Computer, click Folder Options.
Click the View tab.
Clear the Hide extensions for known file types check box.

Right-click the SR.INF file, and then click Install
Windows will now attempt to reinstall System Restore, and may prompt you for the Windows installation source path. Point to %Windir%\ServicePackFiles folder, or insert your slipstreamed Windows XP (matching the Service Pack level of your system.)
System Restore core files will be reinstalled. Restart Windows when prompted.

Huge problem with my XP

2008-10-20T02:31:00.000-07:00

Now in Windows XP we have a much more refined protection of these important files....

This system is called:

Windows File Protection

By default, Windows File Protection is always enabled and allows Windows
digitally signed files to replace existing files safely. Currently, signed files are distributed
through:

# Windows Service Packs

# Hotfix distributions

# Operating system upgrades

# Windows Update

# Windows Device Manager

If you introduce a file replacement in any other way, Windows File protection will overwrite your file!

An important part of Windows File Protection is the command line utility:

System File Checker (sfc.exe)

You will often see references to scannow sfc in online newsgroups etc. This is a great tool for troubleshooting Windows XP problems.

How to use Scannow sfc...

The main reason for using this utility is when you suspect there may be a problem with a Windows XP system file.

Perhaps you get a dialog box appear informing you of a problem with a .dll file, or your program will just not load! It is therefore worth checking to see if there are any corrupt system files using scannow sfc.

To do this simply go to the Run box on the Start Menu and type in:

sfc /scannow

This command will immediately initiate the Windows File Protection service to scan all protected files and verify their integrity, replacing any files with which it finds a problem.

The following should appear to give an indication of how long the process is taking.

In an ideal world that would be the end of the story... Any corrupt, missing or incorrect files would be replaced by this process.

However, things can go wrong and the following guide should help!

The #1 complaint with scannow sfc is the following dialog box appearing:

Why does this happen?

Well, in your computer's registry, are several settings that are checked when you run scannow sfc.

As mentioned earlier in this article, the Windows File Protection service constantly monitors for any changes to the main system files. Well Windows XP keeps a cache (copy) of these essential files at the following location:

C:WINDOWS\System32\Dllcache (assuming C: is your system root which it probably is.)

NB - The dllcache folder is extremely important so Windows XP hides it from you! To view it go to: My Computer > Tools > Folder Options > View > "uncheck" Hide protected operating system files.

If that's the case on your computer then there is normally no need for the original XP CD to be inserted as your computer has a "copy" it can get hold of in this cache...

But, if the Dllcache folder, or part of it, has become corrupted for some reason then you will be prompted for the XP CD - so your computer can get a clean copy!

Having said that not ALL installations of Windows XP have ALL the system files cached into this folder! You may only have around 50MB of files in this folder under Windows XP depending on the quota settings in the registry. (Under Windows 2003 Server the default is 300MB of system files!)

Annoying, YES!

Is there a workaround YES!

As well as having a cache of all the system files on your PC, I like to have the I386 folder from the XP CD installed on the computer as well. After doing this I then modify the registry to tell it the source path for these files... Why? Well not only does this prevent 99% of request for the the XP CD with Windows File Protection. But the I386 folder also contains many other files that are sometimes needed by the operating system and this stops those requests for the XP CD too!

NB - With today's large hard drives you are not going to notice this 475 MB folder on your computer, but older systems may not have the space for this...

Step 1

You will need to get your XP CD and locate the folder called:

I386

This is a major folder and should be one of the first you see, now copy this onto your hard drive into the system root. For most of you that is going to be C:\ so you should end up with a folder that looks like: C:\I386

-----------------------------

Step 2

Now you will need to tell your computer you now have the files on your PC. We do this is the registry (type regedit in the Run box on the start menu) by navigating to:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\
CurrentVersion\Setup

You will see various entries here on the right hand side. The one we want is called:

SourcePath

It probably has an entry pointing to your CD-ROM drive, and that is why it is asking for the XP CD. All we need to do is change it to:

C:\

Simply double click the SourcePatch setting and a new box will pop up allowing you to make the change.

Now restart your computer and try scannow sfc again!

------------------------------

What about Windows Updates.....

You may be asking yourself how does sfc.exe know how to check for updated Windows system files? Well during OS upgrades, service pack installations etc.. the dllcache folder should be updated with these new files.

As an example the recent Windows XP Hotfix - KB828035 updated the system file wkssvc.dll A new version of the file was placed in C:\WINDOWS\system32 and a copy in the cache: C:\WINDOWS\system32\dllcache A copy of the old system file is archived in: C:\WINDOWS\$NtUninstallKB828035$

There is another location the Windows File protection service uses and that is the I386 folder in C:\WINDOWS\ServicePackFiles When you install a service pack, like SP1. Any new system drivers are cached in this location too.

If you have odd problems with running scannow sfc and nothing else in the article has resolved it, then take a look at the entry in:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\
CurrentVersion\Setup
\ServicePackSourcePath

This should be pointing to the location C:\WINDOWS\ServicePackFiles (assuming C:\ is the boot drive.)

-------------------------------------------------------

For those of you who are familiar with sfc.exe under Windows 2000 professional. It is worth noting that the following two options are NOT available under Windows XP.

These are:

sfc /cancel - In Windows 2000, this command immediately cancels all pending scans of protected system files. This option has no effect in Windows XP.

sfc /quiet - In Windows 2000 this sets Windows File Protection to replace any incorrect system files detected with the appropriate version from the dll cache without any user notification. This option has no effect in Windows XP.

Thanks for reading this article on scannow sfc.

what is computer

2008-10-20T02:29:00.001-07:00

what is a computer?

The first sentence should be something like: "A computer is an information processing machine which is capable of simulating any other information processing machine that can fit into its memory." There are three salient parts to the definition:

 -information processing machine
-capable of simulating any other ( like a Universal Turing Machine )
-can be built in real life, so can't have infinite memory ( unlike a Universal Turing Machine )

Currently the first sentence of the article says "A computer is a machine that manipulates data according to a list of instructions", which is only one particular (but dominant) category of computer architecture -- Instruction Set Architecture. Other real life categories which are actually sold are:

 parallel/multi-core -- one computer processes many lists of instructions in parallel
reconfigurable/FPGA -- the computer is specialized for simulating any logic network

And some other classes which have only had prototypes:

 stream processors
cellular automata simulators (probably only one of these was ever made (Margolis))
dna computer  —Preceding unsigned comment added by 70.20.219.7 (talk) 03:31, 25 January 2008 (UTC)

While your opening would probably stand up better as a formal definition, I'm not sure that's the best route to follow for an article which is intended to be an accessible introduction to computers. Remember, this article isn't about theories of computation or computability, but about "computers". The term "computer" has a vernacular meaning to society which is every bit as significant as the formal basis. The writing of the article tries to balance these two worlds by introducing computers in fairly familiar terms and then branching out slightly into instruction set (or Von Neumann) architecture. I believe this is a good approach because, as you state, this is the dominant realization of computers and will cover most anything that a typical person will think of as a computer (thread-level parallelism really doesn't break significantly from the "list of instructions" concept, either). With some of your examples (stream processors, special-purpose logic and DSP, DNA computing, etc), there's probably a good bit that can be said about whether these even are computers (the classical "where is the line between a computer and a calculator" question). We run into the issue of a heavily overloaded term in "computer", so we took the tact of making an article as accessible yet informative as possible to a general reader. I really think it would only complicate matters to try to introduce much computing theory in this article, especially since there are a lot of other articles dedicated to the theoretical aspects of computers. -- 74.160.99.252 (talk) 19:07, 11 February 2008 (UTC)

A computer can't be a machine, because the Wikipedia entry for machine excludes computers.Heikediguoren (talk) 21:14, 10 July 2008 (UTC)

The Wiki article for machine is in grave error and should be corrected; analog and digital computers both fall under the broader category of "machines". See Association for Computing Machinery, "the world's first scientific and educational computing society" (and still going strong).

The 3rd edition of the Concise Encyclopedia of Science and Technology (Sybil P. Parker ed., 1994, McGraw-Hill) defines "computer" as "A device that receives, processes and presents information. The two basic types of computers are analog and digital." (Note: A computer doesn't require "a list of instructions".) A broad definition indeed, but the introductory paragraph can quickly set aside the analog variety, which are still in heavy use, although we don't commonly think of them as "computers". Any analog meter, gage, motor driven clock, speedometer, odometer, etc. qualifies as a computer.

I'm not sure "Modern computers are based on tiny integrated circuits…" is the proper phrasing. How about, "Modern electronic computers rely on integrated circuits…" The CPUs in PCs and Macs aren't so "tiny" – it's a relative term anyway.

Btw, the caption that reads, "Microprocessors are miniaturized devices that often implement stored program CPUs" is all wrong; it doesn't even make sense. Microprocessors are literally integrated circuit (as opposed to discrete circuit) electronic computers – computers on a chip. And "central processing unit" should appear earlier in the text. As is, we see "CPU" before we're told what the letters stand for.

computer history

2008-10-20T02:16:00.000-07:00

History of computing

The Jacquard loom was one of the first programmable devices.

It is difficult to identify any one device as the earliest computer, partly because the term "computer" has been subject to varying interpretations over time. Originally, the term "computer" referred to a person who performed numerical calculations (a human computer), often with the aid of a mechanical calculating device.

The history of the modern computer begins with two separate technologies - that of automated calculation and that of programmability.

Examples of early mechanical calculating devices included the abacus, the slide rule and arguably the astrolabe and the Antikythera mechanism (which dates from about 150-100 BC). Hero of Alexandria (c. 10–70 AD) built a mechanical theater which performed a play lasting 10 minutes and was operated by a complex system of ropes and drums that might be considered to be a means of deciding which parts of the mechanism performed which actions and when.^[3] This is the essence of programmability.

The "castle clock", an astronomical clock invented by Al-Jazari in 1206, is considered to be the earliest programmable analog computer.^[4] It displayed the zodiac, the solar and lunar orbits, a crescent moon-shaped pointer travelling across a gateway causing automatic doors to open every hour,^[5]^[6] and five robotic musicians who play music when struck by levers operated by a camshaft attached to a water wheel. The length of day and night could be re-programmed every day in order to account for the changing lengths of day and night throughout the year.^[4]

The end of the Middle Ages saw a re-invigoration of European mathematics and engineering, and Wilhelm Schickard's 1623 device was the first of a number of mechanical calculators constructed by European engineers. However, none of those devices fit the modern definition of a computer because they could not be programmed.

In 1801, Joseph Marie Jacquard made an improvement to the textile loom that used a series of punched paper cards as a template to allow his loom to weave intricate patterns automatically. The resulting Jacquard loom was an important step in the development of computers because the use of punched cards to define woven patterns can be viewed as an early, albeit limited, form of programmability.

It was the fusion of automatic calculation with programmability that produced the first recognizable computers. In 1837, Charles Babbage was the first to conceptualize and design a fully programmable mechanical computer that he called "The Analytical Engine".^[7] Due to limited finances, and an inability to resist tinkering with the design, Babbage never actually built his Analytical Engine.

Large-scale automated data processing of punched cards was performed for the U.S. Census in 1890 by tabulating machines designed by Herman Hollerith and manufactured by the Computing Tabulating Recording Corporation, which later became IBM. By the end of the 19th century a number of technologies that would later prove useful in the realization of practical computers had begun to appear: the punched card, Boolean algebra, the vacuum tube (thermionic valve) and the teleprinter.

During the first half of the 20th century, many scientific computing needs were met by increasingly sophisticated analog computers, which used a direct mechanical or electrical model of the problem as a basis for computation. However, these were not programmable and generally lacked the versatility and accuracy of modern digital computers.

*Defining characteristics of some early digital computers of the 1940s* (In the history of computing hardware)
Name	First operational	Numeral system	Computing mechanism	Programming	Turing complete
Zuse Z3 (Germany)	May 1941	Binary	Electro-mechanical	Program-controlled by punched film stock	Yes (1998)
Atanasoff–Berry Computer (US)	mid-1941	Binary	Electronic	Not programmable—single purpose	No
Colossus (UK)	January 1944	Binary	Electronic	Program-controlled by patch cables and switches	No
Harvard Mark I – IBM ASCC (US)	1944	Decimal	Electro-mechanical	Program-controlled by 24-channel punched paper tape (but no conditional branch)	No
ENIAC (US)	November 1945	Decimal	Electronic	Program-controlled by patch cables and switches	Yes
Manchester Small-Scale Experimental Machine (UK)	June 1948	Binary	Electronic	Stored-program in Williams cathode ray tube memory	Yes
Modified ENIAC (US)	September 1948	Decimal	Electronic	Program-controlled by patch cables and switches plus a primitive read-only stored programming mechanism using the Function Tables as program ROM	Yes
EDSAC (UK)	May 1949	Binary	Electronic	Stored-program in mercury delay line memory	Yes
Manchester Mark I (UK)	October 1949	Binary	Electronic	Stored-program in Williams cathode ray tube memory and magnetic drum memory	Yes
CSIRAC (Australia)	November 1949	Binary	Electronic	Stored-program in mercury delay line memory	Yes

A succession of steadily more powerful and flexible computing devices were constructed in the 1930s and 1940s, gradually adding the key features that are seen in modern computers. The use of digital electronics (largely invented by Claude Shannon in 1937) and more flexible programmability were vitally important steps, but defining one point along this road as "the first digital electronic computer" is difficult (Shannon 1940). Notable achievements include:

EDSAC was one of the first computers to implement the stored program (von Neumann) architecture.

Konrad Zuse's electromechanical "Z machines". The Z3 (1941) was the first working machine featuring binary arithmetic, including floating point arithmetic and a measure of programmability. In 1998 the Z3 was proved to be Turing complete, therefore being the world's first operational computer.
The non-programmable Atanasoff–Berry Computer (1941) which used vacuum tube based computation, binary numbers, and regenerative capacitor memory.
The secret British Colossus computers (1943)^[8], which had limited programmability but demonstrated that a device using thousands of tubes could be reasonably reliable and electronically reprogrammable. It was used for breaking German wartime codes.
The Harvard Mark I (1944), a large-scale electromechanical computer with limited programmability.
The U.S. Army's Ballistics Research Laboratory ENIAC (1946), which used decimal arithmetic and is sometimes called the first general purpose electronic computer (since Konrad Zuse's Z3 of 1941 used electromagnets instead of electronics). Initially, however, ENIAC had an inflexible architecture which essentially required rewiring to change its programming.

Several developers of ENIAC, recognizing its flaws, came up with a far more flexible and elegant design, which came to be known as the "stored program architecture" or von Neumann architecture. This design was first formally described by John von Neumann in the paper First Draft of a Report on the EDVAC, distributed in 1945. A number of projects to develop computers based on the stored-program architecture commenced around this time, the first of these being completed in Great Britain. The first to be demonstrated working was the Manchester Small-Scale Experimental Machine (SSEM or "Baby"), while the EDSAC, completed a year after SSEM, was the first practical implementation of the stored program design. Shortly thereafter, the machine originally described by von Neumann's paper—EDVAC—was completed but did not see full-time use for an additional two years.

Nearly all modern computers implement some form of the stored-program architecture, making it the single trait by which the word "computer" is now defined. While the technologies used in computers have changed dramatically since the first electronic, general-purpose computers of the 1940s, most still use the von Neumann architecture.

Microprocessors are miniaturized devices that often implement stored program CPUs.

Computers that used vacuum tubes as their electronic elements were in use throughout the 1950s. Vacuum tube electronics were largely replaced in the 1960s by transistor-based electronics, which are smaller, faster, cheaper to produce, require less power, and are more reliable. In the 1970s, integrated circuit technology and the subsequent creation of microprocessors, such as the Intel 4004, further decreased size and cost and further increased speed and reliability of computers. By the 1980s, computers became sufficiently small and cheap to replace simple mechanical controls in domestic appliances such as washing machines. The 1980s also witnessed home computers and the now ubiquitous personal computer. With the evolution of the Internet, personal computers are becoming as common as the television and the telephone in the household.

Stored program architecture

Main articles: Computer program and Computer programming

The defining feature of modern computers which distinguishes them from all other machines is that they can be programmed. That is to say that a list of instructions (the program) can be given to the computer and it will store them and carry them out at some time in the future.

In most cases, computer instructions are simple: add one number to another, move some data from one location to another, send a message to some external device, etc. These instructions are read from the computer's memory and are generally carried out (executed) in the order they were given. However, there are usually specialized instructions to tell the computer to jump ahead or backwards to some other place in the program and to carry on executing from there. These are called "jump" instructions (or branches). Furthermore, jump instructions may be made to happen conditionally so that different sequences of instructions may be used depending on the result of some previous calculation or some external event. Many computers directly support subroutines by providing a type of jump that "remembers" the location it jumped from and another instruction to return to the instruction following that jump instruction.

Program execution might be likened to reading a book. While a person will normally read each word and line in sequence, they may at times jump back to an earlier place in the text or skip sections that are not of interest. Similarly, a computer may sometimes go back and repeat the instructions in some section of the program over and over again until some internal condition is met. This is called the flow of control within the program and it is what allows the computer to perform tasks repeatedly without human intervention.

Comparatively, a person using a pocket calculator can perform a basic arithmetic operation such as adding two numbers with just a few button presses. But to add together all of the numbers from 1 to 1,000 would take thousands of button presses and a lot of time—with a near certainty of making a mistake. On the other hand, a computer may be programmed to do this with just a few simple instructions. For example:

        mov      #0,sum     ; set sum to 0
       mov      #1,num     ; set num to 1
loop:   add      num,sum    ; add num to sum
       add      #1,num     ; add 1 to num
       cmp      num,#1000  ; compare num to 1000
       ble      loop       ; if num <= 1000, go back to 'loop'
       halt                ; end of program. stop running

Once told to run this program, the computer will perform the repetitive addition task without further human intervention. It will almost never make a mistake and a modern PC can complete the task in about a millionth of a second.^[9]

However, computers cannot "think" for themselves in the sense that they only solve problems in exactly the way they are programmed to. An intelligent human faced with the above addition task might soon realize that instead of actually adding up all the numbers one can simply use the equation

and arrive at the correct answer (500,500) with little work.^[10] In other words, a computer programmed to add up the numbers one by one as in the example above would do exactly that without regard to efficiency or alternative solutions.

Programs

A 1970s punched card containing one line from a FORTRAN program. The card reads: "Z(1) = Y + W(1)" and is labelled "PROJ039" for identification purposes.

In practical terms, a computer program may run from just a few instructions to many millions of instructions, as in a program for a word processor or a web browser. A typical modern computer can execute billions of instructions per second (gigahertz or GHz) and rarely make a mistake over many years of operation. Large computer programs comprising several million instructions may take teams of programmers years to write, thus the probability of the entire program having been written without error is highly unlikely.

Errors in computer programs are called "bugs". Bugs may be benign and not affect the usefulness of the program, or have only subtle effects. But in some cases they may cause the program to "hang" - become unresponsive to input such as mouse clicks or keystrokes, or to completely fail or "crash". Otherwise benign bugs may sometimes may be harnessed for malicious intent by an unscrupulous user writing an "exploit" - code designed to take advantage of a bug and disrupt a program's proper execution. Bugs are usually not the fault of the computer. Since computers merely execute the instructions they are given, bugs are nearly always the result of programmer error or an oversight made in the program's design.^[11]

In most computers, individual instructions are stored as machine code with each instruction being given a unique number (its operation code or opcode for short). The command to add two numbers together would have one opcode, the command to multiply them would have a different opcode and so on. The simplest computers are able to perform any of a handful of different instructions; the more complex computers have several hundred to choose from—each with a unique numerical code. Since the computer's memory is able to store numbers, it can also store the instruction codes. This leads to the important fact that entire programs (which are just lists of instructions) can be represented as lists of numbers and can themselves be manipulated inside the computer just as if they were numeric data. The fundamental concept of storing programs in the computer's memory alongside the data they operate on is the crux of the von Neumann, or stored program, architecture. In some cases, a computer might store some or all of its program in memory that is kept separate from the data it operates on. This is called the Harvard architecture after the Harvard Mark I computer. Modern von Neumann computers display some traits of the Harvard architecture in their designs, such as in CPU caches.

While it is possible to write computer programs as long lists of numbers (machine language) and this technique was used with many early computers,^[12] it is extremely tedious to do so in practice, especially for complicated programs. Instead, each basic instruction can be given a short name that is indicative of its function and easy to remember—a mnemonic such as ADD, SUB, MULT or JUMP. These mnemonics are collectively known as a computer's assembly language. Converting programs written in assembly language into something the computer can actually understand (machine language) is usually done by a computer program called an assembler. Machine languages and the assembly languages that represent them (collectively termed low-level programming languages) tend to be unique to a particular type of computer. For instance, an ARM architecture computer (such as may be found in a PDA or a hand-held videogame) cannot understand the machine language of an Intel Pentium or the AMD Athlon 64 computer that might be in a PC.^[13]

Though considerably easier than in machine language, writing long programs in assembly language is often difficult and error prone. Therefore, most complicated programs are written in more abstract high-level programming languages that are able to express the needs of the computer programmer more conveniently (and thereby help reduce programmer error). High level languages are usually "compiled" into machine language (or sometimes into assembly language and then into machine language) using another computer program called a compiler.^[14] Since high level languages are more abstract than assembly language, it is possible to use different compilers to translate the same high level language program into the machine language of many different types of computer. This is part of the means by which software like video games may be made available for different computer architectures such as personal computers and various video game consoles.

The task of developing large software systems is an immense intellectual effort. Producing software with an acceptably high reliability on a predictable schedule and budget has proved historically to be a great challenge; the academic and professional discipline of software engineering concentrates specifically on this problem.

Example

A traffic light showing red.

Suppose a computer is being employed to drive a traffic light. A simple stored program might say:

Turn off all of the lights
Turn on the red light
Wait for sixty seconds
Turn off the red light
Turn on the green light
Wait for sixty seconds
Turn off the green light
Turn on the yellow light
Wait for two seconds
Turn off the yellow light
Jump to instruction number (2)

With this set of instructions, the computer would cycle the light continually through red, green, yellow and back to red again until told to stop running the program.

However, suppose there is a simple on/off switch connected to the computer that is intended to be used to make the light flash red while some maintenance operation is being performed. The program might then instruct the computer to:

Turn off all of the lights
Turn on the red light
Wait for sixty seconds
Turn off the red light
Turn on the green light
Wait for sixty seconds
Turn off the green light
Turn on the yellow light
Wait for two seconds
Turn off the yellow light
If the maintenance switch is NOT turned on then jump to instruction number 2
Turn on the red light
Wait for one second
Turn off the red light
Wait for one second
Jump to instruction number 11

In this manner, the computer is either running the instructions from number (2) to (11) over and over or its running the instructions from (11) down to (16) over and over, depending on the position of the switch.^[15]

How computers work

A general purpose computer has four main sections: the arithmetic and logic unit (ALU), the control unit, the memory, and the input and output devices (collectively termed I/O). These parts are interconnected by busses, often made of groups of wires.

The control unit, ALU, registers, and basic I/O (and often other hardware closely linked with these) are collectively known as a central processing unit (CPU). Early CPUs were composed of many separate components but since the mid-1970s CPUs have typically been constructed on a single integrated circuit called a microprocessor.

Control unit

The control unit (often called a control system or central controller) directs the various components of a computer. It reads and interprets (decodes) instructions in the program one by one. The control system decodes each instruction and turns it into a series of control signals that operate the other parts of the computer.^[16] Control systems in advanced computers may change the order of some instructions so as to improve performance.

A key component common to all CPUs is the program counter, a special memory cell (a register) that keeps track of which location in memory the next instruction is to be read from.^[17]

Diagram showing how a particular MIPS architecture instruction would be decoded by the control system.

The control system's function is as follows—note that this is a simplified description, and some of these steps may be performed concurrently or in a different order depending on the type of CPU:

Read the code for the next instruction from the cell indicated by the program counter.
Decode the numerical code for the instruction into a set of commands or signals for each of the other systems.
Increment the program counter so it points to the next instruction.
Read whatever data the instruction requires from cells in memory (or perhaps from an input device). The location of this required data is typically stored within the instruction code.
Provide the necessary data to an ALU or register.
If the instruction requires an ALU or specialized hardware to complete, instruct the hardware to perform the requested operation.
Write the result from the ALU back to a memory location or to a register or perhaps an output device.
Jump back to step (1).

Since the program counter is (conceptually) just another set of memory cells, it can be changed by calculations done in the ALU. Adding 100 to the program counter would cause the next instruction to be read from a place 100 locations further down the program. Instructions that modify the program counter are often known as "jumps" and allow for loops (instructions that are repeated by the computer) and often conditional instruction execution (both examples of control flow).

It is noticeable that the sequence of operations that the control unit goes through to process an instruction is in itself like a short computer program - and indeed, in some more complex CPU designs, there is another yet smaller computer called a microsequencer that runs a microcode program that causes all of these events to happen.

Arithmetic/logic unit (ALU)

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Main article: Arithmetic logic unit

The ALU is capable of performing two classes of operations: arithmetic and logic.

The set of arithmetic operations that a particular ALU supports may be limited to adding and subtracting or might include multiplying or dividing, trigonometry functions (sine, cosine, etc) and square roots. Some can only operate on whole numbers (integers) whilst others use floating point to represent real numbers—albeit with limited precision. However, any computer that is capable of performing just the simplest operations can be programmed to break down the more complex operations into simple steps that it can perform. Therefore, any computer can be programmed to perform any arithmetic operation—although it will take more time to do so if its ALU does not directly support the operation. An ALU may also compare numbers and return boolean truth values (true or false) depending on whether one is equal to, greater than or less than the other ("is 64 greater than 65?").

Logic operations involve Boolean logic: AND, OR, XOR and NOT. These can be useful both for creating complicated conditional statements and processing boolean logic.

Superscalar computers contain multiple ALUs so that they can process several instructions at the same time. Graphics processors and computers with SIMD and MIMD features often provide ALUs that can perform arithmetic on vectors and matrices.

Memory

Main article: Computer storage

Magnetic core memory was popular main memory for computers through the 1960s until it was completely replaced by semiconductor memory.

A computer's memory can be viewed as a list of cells into which numbers can be placed or read. Each cell has a numbered "address" and can store a single number. The computer can be instructed to "put the number 123 into the cell numbered 1357" or to "add the number that is in cell 1357 to the number that is in cell 2468 and put the answer into cell 1595". The information stored in memory may represent practically anything. Letters, numbers, even computer instructions can be placed into memory with equal ease. Since the CPU does not differentiate between different types of information, it is up to the software to give significance to what the memory sees as nothing but a series of numbers.

In almost all modern computers, each memory cell is set up to store binary numbers in groups of eight bits (called a byte). Each byte is able to represent 256 different numbers; either from 0 to 255 or -128 to +127. To store larger numbers, several consecutive bytes may be used (typically, two, four or eight). When negative numbers are required, they are usually stored in two's complement notation. Other arrangements are possible, but are usually not seen outside of specialized applications or historical contexts. A computer can store any kind of information in memory as long as it can be somehow represented in numerical form. Modern computers have billions or even trillions of bytes of memory.

The CPU contains a special set of memory cells called registers that can be read and written to much more rapidly than the main memory area. There are typically between two and one hundred registers depending on the type of CPU. Registers are used for the most frequently needed data items to avoid having to access main memory every time data is needed. Since data is constantly being worked on, reducing the need to access main memory (which is often slow compared to the ALU and control units) greatly increases the computer's speed.

Computer main memory comes in two principal varieties: random access memory or RAM and read-only memory or ROM. RAM can be read and written to anytime the CPU commands it, but ROM is pre-loaded with data and software that never changes, so the CPU can only read from it. ROM is typically used to store the computer's initial start-up instructions. In general, the contents of RAM is erased when the power to the computer is turned off while ROM retains its data indefinitely. In a PC, the ROM contains a specialized program called the BIOS that orchestrates loading the computer's operating system from the hard disk drive into RAM whenever the computer is turned on or reset. In embedded computers, which frequently do not have disk drives, all of the software required to perform the task may be stored in ROM. Software that is stored in ROM is often called firmware because it is notionally more like hardware than software. Flash memory blurs the distinction between ROM and RAM by retaining data when turned off but being rewritable like RAM. However, flash memory is typically much slower than conventional ROM and RAM so its use is restricted to applications where high speeds are not required.^[18]

In more sophisticated computers there may be one or more RAM cache memories which are slower than registers but faster than main memory. Generally computers with this sort of cache are designed to move frequently needed data into the cache automatically, often without the need for any intervention on the programmer's part.

Input/output (I/O)

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Main article: Input/output

Hard disks are common I/O devices used with computers.

I/O is the means by which a computer receives information from the outside world and sends results back. Devices that provide input or output to the computer are called peripherals. On a typical personal computer, peripherals include input devices like the keyboard and mouse, and output devices such as the display and printer. Hard disk drives, floppy disk drives and optical disc drives serve as both input and output devices. Computer networking is another form of I/O.

Often, I/O devices are complex computers in their own right with their own CPU and memory. A graphics processing unit might contain fifty or more tiny computers that perform the calculations necessary to display 3D graphics^{[citation needed]}. Modern desktop computers contain many smaller computers that assist the main CPU in performing I/O.

Multitasking

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Main article: Computer multitasking

While a computer may be viewed as running one gigantic program stored in its main memory, in some systems it is necessary to give the appearance of running several programs simultaneously. This is achieved by having the computer switch rapidly between running each program in turn. One means by which this is done is with a special signal called an interrupt which can periodically cause the computer to stop executing instructions where it was and do something else instead. By remembering where it was executing prior to the interrupt, the computer can return to that task later. If several programs are running "at the same time", then the interrupt generator might be causing several hundred interrupts per second, causing a program switch each time. Since modern computers typically execute instructions several orders of magnitude faster than human perception, it may appear that many programs are running at the same time even though only one is ever executing in any given instant. This method of multitasking is sometimes termed "time-sharing" since each program is allocated a "slice" of time in turn.

Before the era of cheap computers, the principle use for multitasking was to allow many people to share the same computer.

Seemingly, multitasking would cause a computer that is switching between several programs to run more slowly - in direct proportion to the number of programs it is running. However, most programs spend much of their time waiting for slow input/output devices to complete their tasks. If a program is waiting for the user to click on the mouse or press a key on the keyboard, then it will not take a "time slice" until the event it is waiting for has occurred. This frees up time for other programs to execute so that many programs may be run at the same time without unacceptable speed loss.

Multiprocessing

Main article: Multiprocessing

Cray designed many supercomputers that used multiprocessing heavily.

Some computers may divide their work between one or more separate CPUs, creating a multiprocessing configuration. Traditionally, this technique was utilized only in large and powerful computers such as supercomputers, mainframe computers and servers. However, multiprocessor and multi-core (multiple CPUs on a single integrated circuit) personal and laptop computers have become widely available and are beginning to see increased usage in lower-end markets as a result.

Supercomputers in particular often have highly unique architectures that differ significantly from the basic stored-program architecture and from general purpose computers.^[19] They often feature thousands of CPUs, customized high-speed interconnects, and specialized computing hardware. Such designs tend to be useful only for specialized tasks due to the large scale of program organization required to successfully utilize most of the available resources at once. Supercomputers usually see usage in large-scale simulation, graphics rendering, and cryptography applications, as well as with other so-called "embarrassingly parallel" tasks.

Networking and the Internet

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Main articles: Computer networking and Internet

Visualization of a portion of the routes on the Internet.

Computers have been used to coordinate information between multiple locations since the 1950s. The U.S. military's SAGE system was the first large-scale example of such a system, which led to a number of special-purpose commercial systems like Sabre.

In the 1970s, computer engineers at research institutions throughout the United States began to link their computers together using telecommunications technology. This effort was funded by ARPA (now DARPA), and the computer network that it produced was called the ARPANET. The technologies that made the Arpanet possible spread and evolved. In time, the network spread beyond academic and military institutions and became known as the Internet. The emergence of networking involved a redefinition of the nature and boundaries of the computer. Computer operating systems and applications were modified to include the ability to define and access the resources of other computers on the network, such as peripheral devices, stored information, and the like, as extensions of the resources of an individual computer. Initially these facilities were available primarily to people working in high-tech environments, but in the 1990s the spread of applications like e-mail and the World Wide Web, combined with the development of cheap, fast networking technologies like Ethernet and ADSL saw computer networking become almost ubiquitous. In fact, the number of computers that are networked is growing phenomenally. A very large proportion of personal computers regularly connect to the Internet to communicate and receive information. "Wireless" networking, often utilizing mobile phone networks, has meant networking is becoming increasingly ubiquitous even in mobile computing environments.

Further topics

Hardware

Main article: Computer hardware

The term hardware covers all of those parts of a computer that are tangible objects. Circuits, displays, power supplies, cables, keyboards, printers and mice are all hardware.

**History of computing hardware**
First Generation (Mechanical/Electromechanical)	Calculators	Antikythera mechanism, Difference Engine, Norden bombsight
First Generation (Mechanical/Electromechanical)	Programmable Devices	Jacquard loom, Analytical Engine, Harvard Mark I, Z3
Second Generation (Vacuum Tubes)	Calculators	Atanasoff–Berry Computer, IBM 604, UNIVAC 60, UNIVAC 120
Second Generation (Vacuum Tubes)	Programmable Devices	Colossus, ENIAC, Manchester Small-Scale Experimental Machine, EDSAC, Manchester Mark I, CSIRAC, EDVAC, UNIVAC I, IBM 701, IBM 702, IBM 650, Z22
Third Generation (Discrete transistors and SSI, MSI, LSI Integrated circuits)	Mainframes	IBM 7090, IBM 7080, System/360, BUNCH
	Minicomputer	PDP-8, PDP-11, System/32, System/36
Fourth Generation (VLSI integrated circuits)	Minicomputer	VAX, IBM System i
	4-bit microcomputer	Intel 4004, Intel 4040
	8-bit microcomputer	Intel 8008, Intel 8080, Motorola 6800, Motorola 6809, MOS Technology 6502, Zilog Z80
	16-bit microcomputer	Intel 8088, Zilog Z8000, WDC 65816/65802
	32-bit microcomputer	Intel 80386, Pentium, Motorola 68000, ARM architecture
	64-bit microcomputer^[20]	Alpha, MIPS, PA-RISC, PowerPC, SPARC, x86-64
	Embedded computer	Intel 8048, Intel 8051
	Personal computer	Desktop computer, Home computer, Laptop computer, Personal digital assistant (PDA), Portable computer, Tablet computer, Wearable computer
Theoretical/experimental	Quantum computer, Chemical computer, DNA computing, Optical computer, Spintronics based computer

**Other Hardware Topics**
Peripheral device (Input/output)	Input	Mouse, Keyboard, Joystick, Image scanner
	Output	Monitor, Printer
	Both	Floppy disk drive, Hard disk, Optical disc drive, Teleprinter
Computer busses	Short range	RS-232, SCSI, PCI, USB
Computer busses	Long range (Computer networking)	Ethernet, ATM, FDDI

Software

Main article: Computer software

Software refers to parts of the computer which do not have a material form, such as programs, data, protocols, etc. When software is stored in hardware that cannot easily be modified (such as BIOS ROM in an IBM PC compatible), it is sometimes called "firmware" to indicate that it falls into an uncertain area somewhere between hardware and software.

**Computer software**
Operating system	Unix/BSD	UNIX System V, AIX, HP-UX, Solaris (SunOS), IRIX, List of BSD operating systems
	GNU/Linux	List of Linux distributions, Comparison of Linux distributions
	Microsoft Windows	Windows 95, Windows 98, Windows NT, Windows 2000, Windows XP, Windows Vista, Windows CE
	DOS	86-DOS (QDOS), PC-DOS, MS-DOS, FreeDOS
	Mac OS	Mac OS classic, Mac OS X
	Embedded and real-time	List of embedded operating systems
	Experimental	Amoeba, Oberon/Bluebottle, Plan 9 from Bell Labs
Library	Multimedia	DirectX, OpenGL, OpenAL
Library	Programming library	C standard library, Standard template library
Data	Protocol	TCP/IP, Kermit, FTP, HTTP, SMTP
Data	File format	HTML, XML, JPEG, MPEG, PNG
User interface	Graphical user interface (WIMP)	Microsoft Windows, GNOME, KDE, QNX Photon, CDE, GEM
User interface	Text user interface	Command line interface, shells
Application	Office suite	Word processing, Desktop publishing, Presentation program, Database management system, Scheduling & Time management, Spreadsheet, Accounting software
	Internet Access	Browser, E-mail client, Web server, Mail transfer agent, Instant messaging
	Design and manufacturing	Computer-aided design, Computer-aided manufacturing, Plant management, Robotic manufacturing, Supply chain management
	Graphics	Raster graphics editor, Vector graphics editor, 3D modeler, Animation editor, 3D computer graphics, Video editing, Image processing
	Audio	Digital audio editor, Audio playback, Mixing, Audio synthesis, Computer music
	Software Engineering	Compiler, Assembler, Interpreter, Debugger, Text Editor, Integrated development environment, Performance analysis, Revision control, Software configuration management
	Educational	Edutainment, Educational game, Serious game, Flight simulator
	Games	Strategy, Arcade, Puzzle, Simulation, First-person shooter, Platform, Massively multiplayer, Interactive fiction
	Misc	Artificial intelligence, Antivirus software, Malware scanner, Installer/Package management systems, File manager

Programming languages

Programming languages provide various ways of specifying programs for computers to run. Unlike natural languages, programming languages are designed to permit no ambiguity and to be concise. They are purely written languages and are often difficult to read aloud. They are generally either translated into machine language by a compiler or an assembler before being run, or translated directly at run time by an interpreter. Sometimes programs are executed by a hybrid method of the two techniques. There are thousands of different programming languages—some intended to be general purpose, others useful only for highly specialized applications.

**Programming Languages**
Lists of programming languages	Timeline of programming languages, Categorical list of programming languages, Generational list of programming languages, Alphabetical list of programming languages, Non-English-based programming languages
Commonly used Assembly languages	ARM, MIPS, x86
Commonly used High level languages	BASIC, C, C++, C#, COBOL, Fortran, Java, Lisp, Pascal
Commonly used Scripting languages	Bourne script, JavaScript, Python, Ruby, PHP, Perl

Professions and organizations

As the use of computers has spread throughout society, there are an increasing number of careers involving computers. Following the theme of hardware, software and firmware, the brains of people who work in the industry are sometimes known irreverently as wetware or "meatware".

**Computer-related professions**
Hardware-related	Electrical engineering, Electronics engineering, Computer engineering, Telecommunications engineering, Optical engineering, Nanoscale engineering
Software-related	Computer science, Human-computer interaction, Information technology, Software engineering, Scientific computing, Web design, Desktop publishing

The need for computers to work well together and to be able to exchange information has spawned the need for many standards organizations, clubs and societies of both a formal and informal nature.

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2008-10-11T03:41:00.000-07:00

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DOEACC Online E-Books and Notes

Computer Abbreviations and Names

shortcut for microsoft words

MOVING THE TEXT

COPYING THE TEXT

UNDO, REDO AND REPEAT

FUNCTION, ICON AND SHORTCUT KEYS

SOME SHORTCUT KEYS FOR FORMATTING

Reinstalling System

Reinstalling System Restore

Huge problem with my XP

Why does this happen?

Other Problems with scannow sfc...

What about Windows Updates.....

what is computer

what is a computer?

computer history

History of computing

Stored program architecture

Programs

Example

How computers work

Control unit

Arithmetic/logic unit (ALU)

Memory

Input/output (I/O)

Multitasking

Multiprocessing

Networking and the Internet

Further topics

Hardware

Software

Programming languages

Professions and organizations

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